Aluminum composite material having neutron-absorbing ability

ABSTRACT

The present invention provides an aluminum composite material having neutron absorbing power that improves the ability to absorb neutrons by increasing the content of B, while also being superior to materials of the prior art in terms of mechanical properties and workability. The aluminum composite material having neutron absorbing power contains in Al or an Al alloy matrix phase B or a B compound having neutron absorbing power in an amount such that the proportion of B is 1.5% by weight or more to 9% by weight or less, and the aluminum composite material has been pressure sintered.

TECHNICAL FIELD

The present invention relates to an aluminum composite material havingneutron absorbing power that is useful as, for example, a structuralmaterial of a transport container or storage container and so forth ofspent nuclear fuel, and its production method.

BACKGROUND ART

Although boron (B) is an element that has the action of absorbingneutrons, only the ¹⁰B isotope, which is present at a proportion ofabout 20% in naturally-occurring B, is known to actually have saidaction. Alloys in which B is added to an Al alloy have been used in thepast as structural materials having neutron absorbing action.

Ordinary melting methods have been employed in the case of producingsuch an alloy. Since the liquidus temperature rises rapidly as theamount of B added increases however, various methods are used, includingadding B to the Al alloy in the form of a powder or Al—B alloy, adding Bto an Al melt in the form of a borofluoride such as KBF₄ to form an Al—Bintermetallic compound, and using a casting or pressurized castingmethod starting at a temperature equal to or below the liquidustemperature at which both liquid and solid are present. However, variousimprovements have been made to enhance mechanical properties such asstrength and ductility. There are numerous examples of theseimprovements, some of which include Japanese Unexamined PatentApplication, First Publication No. Sho 59-501672, Japanese UnexaminedPatent Application, First Publication No. Sho 61-235523, JapaneseUnexamined Patent Application, First Publication No. Sho 62-70799,Japanese Unexamined Patent Application, First Publication No. Sho62-235437, Japanese Unexamined Patent Application, First Publication No.Sho 62-243733, Japanese Unexamined Patent Application, First PublicationNo. Sho 63-312943, Japanese Unexamined Patent Application, FirstPublication No. Hei 1-312043, Japanese Unexamined Patent Application,First Publication No. No. Hei 1-312044 and Japanese Unexamined PatentApplication, First Publication No. Hei 9-165637.

In Al—B alloy according to this type of melting method, when B is addedthat absorbs neutrons, intermetallic compounds such as AlB₂ and AlB₁₂are present as B compounds, and when a large amount of AlB₁₂ inparticular is present, workability decreases. However, since it istechnically difficult to control the amount of this AlB₁₂, addition ofthe amount of B up to 1.5% by weight is the limit for practically usedmaterials, and thus, neutron absorbing effects are not that large.

In addition, borals are materials other than the Al—B alloy according tothe melting methods described above that have neutron absorbing action.This boral is a material in which a powder, in which 30-40% by weight ofB₄C is blended into an Al matrix material, is sandwiched followed byrolling. However, not only is the tensile strength of this boral low atabout 40 MPa, since its elongation is also low at 1% making molding andforming difficult, it is currently not used as a structural material.

An example of a production method of Al—B₄C composite materials thatstill leaves something to be desired involves the use of powdermetallurgy. This method consists of uniformly mixing Al alloy and B₄Cboth in the state of a powder followed by solidifying and molding. Inaddition to being able to avoid the above problems accompanying melting,this method offers advantages including greater freedom in selecting thematrix composition. In U.S. Pat. No. 5,486,223 and a series of followingpatents by the same inventor, a method is described for obtaining anAl—B₄C composite material having superior strength characteristics usinga powder metallurgy method. In particular, U.S. Pat. No. 5,700,962focuses on the production of a neutron-blocking material. However, inthese inventions, due to the use of a special B₄C to which specificelements are added to improve binding with the matrix, the process iscomplex, and there were considerable problems in terms of cost forpractical application. In addition, there were also numerous areas ofconcern with respect to performance, such as the occurrence of gascontamination as a result of heating and extrusion of a porous moldedarticle in which the powder is solidified with CIP only, and significantdeterioration of characteristics as a result of exposing to a hightemperature of 625° C. or higher during billet sintering depending onthe matrix composition.

As described above, since there are limitations on the added amount of acompound having neutron absorbing power such as B in Al alloy producedwith a melting method, the neutron absorbing effects were small. Inorder to resolve this problem, although numerous inventions have beenmade as mentioned above, in order to work those inventions, there weremany prerequisites that considerably raised production cost, includingmelting a master alloy in which the ratios of internal compound phases(AlB₂, AlB₁₂ and others) have been controlled, and using extremelyexpensive concentrated boron, thus making these inventions difficult toapply practically at the industrial level. In addition, in terms of theoperation, the working of these inventions with ordinary Al meltingequipment has been nearly practically impossible due to problems such ascontamination of the inside of the furnace (such as requiring that thefurnace be washed to remove dross having a high B concentration, andcontamination resulting from residual fluorides that were loaded intothe furnace), and damage to the furnace materials caused by a highmelting temperature (requiring a temperature of 1200° C. and above insome cases).

In addition, a boral having a high B₄C content of 30-40% by weight hasproblems with workability, preventing it from being used as a structuralmaterial.

In consideration of these background circumstances, in addition toseeking high neutron absorbing power by increasing the content of B,there has been a need for an aluminum composite material having neutronabsorbing power, and its production method, that has superior mechanicalproperties such as tensile strength and elongation, is easily worked andcan be used as a structural material.

DISCLOSURE OF INVENTION

Therefore, the object of the present invention is to provide an aluminumcomposite material having neutron absorbing power, and its productionmethod, that enables the neutron absorbing power to be enhanced byincreasing the B content, and is superior in terms of mechanicalproperties and workability.

In consideration of the present circumstances as described above,together with creating a method for inexpensively producing an Alcomposite material that satisfies the necessary neutron absorbing powerand strength characteristics in the proper balance by using ordinaryinexpensive B₄C available on the market as an abrasive or refractorymaterial, the inventors of the present invention found an alloycomposition (including the amount of B₄C added) in which the maximumeffects of this method are demonstrated.

The present invention employed the following means to solve the aboveproblems.

An aluminum composite material having neutron absorbing power of thepresent invention is characterized in that it contains in Al or an Alalloy matrix phase B or a B compound having neutron absorbing power inan amount such that the proportion of B is 1.5% by weight or more to 9%by weight or less, and that the aluminum composite material has beenpressure sintered.

In this case, the B or B compound having neutron absorbing powercontained in the Al or Al alloy matrix phase is preferably such that theproportion of B is 2% by weight or more and 5% by weight or less.

According to this aluminum composite material having neutron absorbingpower, the amount of B or B compound added is high, and tensilecharacteristics and other mechanical properties are superior. Inaddition, its production cost can be held to a low level.

The production method of an aluminum composite material having neutronabsorbing power of the present invention comprises adding a B or Bcompound powder having neutron absorbing power in an amount such thatthe proportion of B is 1.5% by weight or more to 9% by weight or less toan Al or Al alloy powder, and pressurized sintering the powder.

In this case, it is preferable to use a rapidly solidified powder havinga uniform, fine composition for the Al or Al alloy powder, while boroncarbide (B₄C) particles are preferably used as the B compound powder.The mean particle size of the above Al or Al alloy powder is preferably5-150 μm, and B₄C particles having a mean particle size of 1-60 μm arepreferably used as the B compound particles used.

In addition, hot extrusion, hot rolling, hot hydrostatic pressing or hotpressing, or any of their combinations, can be used as the method ofpressurized sintering.

These pressurized sintering methods are all characterized by charging apowder into a can (canning) followed by drawing a vacuum while heatingto remove the gas components and moisture adsorbed on the surface of thepowder inside the can, and finally sealing the can. This canned powderis then subjected to heat processing while maintaining the vacuum insidethe can.

Moreover, after performing the above pressurized sintering, heattreatment is preferably suitably performed as necessary.

According to this production method of an aluminum composite materialhaving neutron absorbing power, by employing a powder metallurgy methodusing pressurized sintering, an aluminum composite material can beproduced that has superior tensile characteristics and other mechanicalproperties even if the amount of B or B compound added is increased.Thus, an aluminum composite material can be provided that is able toimprove neutron absorbing power while also having superior workability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph relating to the mechanical properties of an Alcomposite material having neutron absorbing power according to thepresent invention, and shows the relationship between 0.2% yieldstrength (MPa) and temperature (°C.) for samples F, G and I of Table 2.

FIG. 2 is a graph relating to the mechanical properties of an Alcomposite material having neutron absorbing power according to thepresent invention that shows the relationship between tensile strength(MPa) and temperature (° C.) for samples F, G and I of Table 2.

FIG. 3 is a graph relating to the mechanical properties of an Alcomposite material having neutron absorbing power according to thepresent invention that shows the effects of the amount of B added atroom temperature for pure Al-based composite materials (samples Athrough E of Table 2).

FIG. 4 is a graph relating to the mechanical properties of an Alcomposite material having neutron absorbing power according to thepresent invention that shows the effects of the amount of B added atroom temperature for Al—6Fe-based composite materials (samples H throughL of Table 2).

FIG. 5 is a graph relating to the mechanical properties of an Alcomposite material having neutron absorbing power according to thepresent invention that shows the effects of the amount of B added at250° C. for Al—6Fe-based composite materials (samples H through L ofTable 2).

BEST MODE FOR CARRYING OUT THE INVENTION

The following provides an explanation of an embodiment of an aluminumcomposite material, and its production method, having neutron absorbingpower as claimed in the present invention, along with a description ofthe reasons for limiting the ranges of each parameter.

The production method of an Al composite material in the presentinvention involves mixing an Al or Al alloy powder produced with a rapidsolidification method such as atomization with a B or B compound powderhaving neutron absorbing power followed by pressurized sintering. Here,the amount of B added is within the range of 1.5% by weight or more to9% by weight or less.

Examples of the Al or Al alloy powder that can be used as the baseinclude pure aluminum metal (JIS 2xxx series), Al—Mg-based aluminumalloy (JIS 5xxx series), Al—Mg—Si-based aluminum alloy (JIS 6xxxseries), Al—Zn—Mg-based aluminum alloy (JIS 7xxx series) and Al—Fe-basedaluminum alloy (having an Fe content of 1-10% by weight), as well asAl—Mn-based aluminum alloy (JIS 3xxx series). There are no particularrestrictions on the base, and it can be selected according to therequired characteristics such as strength, ductility, workability andheat resistance.

Rapidly solidified powders having a uniform, fine structure are used asthese Al or Al alloys. Examples of rapid solidification methods that canbe employed for obtaining this rapidly solidified powder include knowntechnologies such as single rolling, dual rolling or air atomization,gas atomization and other atomization methods. The Al alloy powderobtained by rapid solidification in this manner is preferably used thathas a mean particle size of 5-150 μm.

The reason for this is that, since the particles end up aggregating dueto being in the form of fine particles if the mean particle size is lessthan 5 μm, the particles eventually take on the form of large clumps andplace limitations on production by atomization (because it becomesnecessary to remove only fine particles, the powder production yield isworsened considerably resulting in a sudden increase in costs). If themean particle size exceeds 150 μm, there are limitations on product byatomization since they are no longer solidify by rapid-cooling. Inaddition, there are also problems in terms of the difficulty inuniformly mixing with fine added particles. Thus, the most preferablemean particle size is 50-120 μm.

The rapid cooling rate of rapid solidification is 10²° C./sec or more,and preferably 10³° C./sec or more.

On the other hand, the B or B compound mixed with the above Al or Alalloy powder has the characteristic of having the ability to absorbparticularly high-speed neutrons. Furthermore, examples of preferable Bcompounds that can be used in the present invention include B₄C andB₂O₃. B₄C in particular has a high B content per unit amount, and allowsthe obtaining of powerful neutron absorbing power even if added in smallamounts. In addition, it is particularly preferable as a particle addedto structural materials having an extremely high hardness and so forth.

The amount added of this B or B compound is such that the proportion ofB in percent by weight is 1.5 or more to 9 or less, and preferably 2 ormore to 5 or less. The reason for this is as described below.

In the case of considering the use of aluminum alloy (and aluminum-basedcomposite material) as a structural material in the field of nuclearpower, and more specifically, as a structural material of a storage ortransport container of spent nuclear fuel, the thickness of the membersis necessarily from about 5 to 30 mm. In the case of a thick-walledmaterial that exceeds this range, it becomes pointless to use a lightaluminum alloy, while on the other hand, in order to secure adequatereliability required by structural materials, it is clear that it wouldbe difficult to use an extremely thin-walled member in consideration ofthe ordinary strength of aluminum alloy. In other words, the neutronblocking ability of the aluminum alloy used in such applications shouldbe an adequate required value over the above range of thickness, andaddition of extremely large amounts of B or B₄C as described in someprevious inventions only serve to unnecessarily worsen workability ordecrease ductility.

According to experiments conducted by the inventors of the presentinvention, in the case of using ordinary B₄C available at an inexpensiveprice on the market for the B source, optimum characteristics for thetarget application are only obtained in the case the amount of B₄C addedis 2-12% by weight, or 1.5-9% by weight in terms of the amount of B. Ifthe amount of B₄C is less than this amount, the required neutronabsorbing power is not obtained. On the other hand, if B₄C is added inexcess of the above range, not only does production become difficult dueto the formation of cracks and so forth during extrusion and othermolding processes, the resulting material has low ductility and isunable to secure the required reliability as a structural material.

In addition, a B or B compound powder is used that preferably has a meanparticle size of 1-60 μm. The reason for this is that, since eachparticle aggregates due to being in the form of a fine powder if themean particle size is less than 1 μm, the powder ultimately takes on theform of large clumps, thereby preventing the obtaining of a uniformdispersion and having an extremely detrimental effect on yield. If meanparticle size exceeds 60 μm, not only does the powder become acontaminant which lowers the material strength and ease of extrusion, italso ends up worsening the cutting workability of the material.

After mixing the above Al or Al alloy powder with the above B or Bcompound powder, an Al alloy composite material is produced byperforming pressurized sintering. Hot extrusion, hot rolling, hothydrostatic pressing (HIP), hot pressing or any of these combinationscan be employed for the pressurized sintering production method.

Furthermore, the preferable heating temperature during pressurizedsintering is 350-550° C.

In addition, one of the characteristics of the present invention isthat, prior to providing a mixed powder for pressurized sintering, thepowder is charged into a can made of Al alloy followed by degassing byheating in a vacuum. If this step is omitted, the amount of gas in thefinally obtained material is excessively large, which prevents thedesired mechanical properties from being obtained, or causes theformation of blistering in the surface during heat treatment. Thepreferable temperature range of vacuum heating degassing is 350-550° C.If this is performed below the lower limit temperature, adequatedegassing effects are unable to be obtained, and if performed at atemperature higher than the upper limit temperature, characteristics maydeteriorate considerable depending on the material.

Following pressurized sintering, heat treatment is performed asnecessary. In the case of, for example, using a powder based on anAl—Mg—Si-based aluminum alloy powder, JIS T6 treatment is performed, andin the case of using a powder based on Al—Cu-based Al alloy powder, JIST6 treatment is also similarly performed. However, in the case of usinga powder based on pure Al or Al—Fe-based Al alloy powder, heat treatmentis not necessary, and JIS T1 treatment is applicable in such cases.

As a result of employing this production method, an aluminum compositematerial can be obtained by pressurized sintering that contains in an Alor Al alloy matrix phase a B or B compound having neutron absorbingpower in an amount such that the proportion of B is 1.5% by weight ormore to 9% by weight or less.

Furthermore, although B or B compounds are known to have superiorhigh-speed neutron absorbing power, a composite material may also beobtained that contains Gd or Gd compound, which has superior low-speedneutron absorbing power, by suitably adding such as necessary.

EXAMPLES

The following provides a detailed explanation of the present inventionby indicating specific experimental examples. In this experiment, Al—B₄Cparticle composite materials were produced by powder metallurgy followedby examination of their mechanical properties.

(1) The Following Four Types were Used as Aluminum or Aluminum AlloyPowder Serving as the Base

Base (1): A powder was obtained by air atomization using a pure Al metalhaving a purity of 99.7%. This is referred to as “pure Al”.

Base (2): A powder was obtained by N₂ gas atomization using an Al alloyhaving a standard composition (wt %) of Al—0.6Si—0.25Cu—1.0Mg—0.25Cr(JIS 6061). This was used after classifying to 150 μm or less (mean: 95μm). This is referred to as “6061Al (Al—Mg—Si series)”.

Base (3): A powder was obtained by N₂ gas atomization using an Al alloyhaving a standard composition (wt %) ofAl—6.3Cu—0.3Mn—0.06Ti—0.1V—0.18Zr (JIS 2219). This was used afterclassifying to 150 μm or less (mean: 95 μm). This is referred to as“2219Al (Al—Cu series)”.

Base (4): A powder was obtained by N₂ gas atomization using anAl—Fe-based Al alloy having a standard composition (wt %) of Al—6Fe.This was used after classifying to 150 μm or less (mean: 95 μm). This isreferred to as “Fe-based Al”.

(2) Commercially Available B₄C Shown in Table 1 was Used as the AddedParticles

TABLE 1 Name (Type) Mean particle size (1) For metal addition 23 μm (2)For metal addition 0.8 μm (3) #800 for polishing 9 μm (4) #280 forpolishing 59 μm (5) #250 for polishing 72 μm

Example 1

<Powders Used>

Here, pure Al powder classified to 250 μm or less (mean: 118 μm), andeach of the powders of 6061Al, 2219Al and Fe-based Al classified to 150μm or less (mean: 95 μm) were used. In addition, B₄C for metal additionhaving a mean particle size of 23 μm was used as the added particles.

<Sample Production>

(1) In the First Stage, the Above Powders and Added Particles were Mixedfor 10-15 Minutes Using a Cross Rotary Mixer

Furthermore, in this experiment, although 12 types of samples wereproduced, the combinations of bases (1) through (4) and added particles(indicated with the value determined by calculating the weight percentof B) are as shown in Table 2.

TABLE 2 Mixed powders Amount of B₄C added Sample (as wt % Heat No. Baseof B) treatment Remarks A Pure Al 0   No (T1) Comparative alloy B PureAl 2.3 No (T1) Alloy of present invention C Pure Al 4.7 No (T1) Alloy ofpresent invention D Pure Al 9.0 No (T1) Alloy of present invention EPure Al 11.3  No (T1) Comparative alloy F 6061Al 2.3 Yes (T6) Alloy ofpresent invention G 2219Al 2.3 Yes (T6) Alloy of present invention HFe-based Al 0   None (T1) Comparative alloy I Fe-based Al 2.3 None (T1)Alloy of present invention J Fe-based Al 4.7 None (T1) Alloy of presentinvention K Fe-based Al 9.0 None (T1) Alloy of present invention LFe-based Al 11.3  None (T1) Comparative alloy

In the second stage, a mixture of base powder and added particles ischarged into a can and canning is performed. The specifications of thecan used here are as shown below.

Material: JIS 6063 (aluminum alloy seamless tube with a bottom plate ofthe same material welded around its entire circumference)

Diameter: 90 mm

Can thickness: 2 mm

In the third stage, vacuum heating degassing is performed. The cannedpowder mixture is heated to 480° C. and a vacuum is drawn inside the canto 1 Torr or less and held for 2 hours. As a result of performing thisdegassing step, gas components and moisture adhered to the surface ofthe powder inside the can are removed, thereby completing production ofthe material for extrusion (to be referred to as the billet).

(2) Extrusion

In this step, the billet produced with the above procedure is hotextruded using a 500 ton extruder. The temperature in this case is 430°C., and the billet was molded into an extruded shape in the form of aflat plate as indicated below using an extrusion ratio of about 12.

Extruded shape (cross-section)

Width: 48 mm

Thickness: 12 mm

(3) Heat Treatment (T6 Treatment)

In this experiment, heat treatment was only performed on samples F and Gshown in Table 2 following extrusion molding.

In the heat treatment of sample F, after performing solution heattreatment for 2 hours at 530° C., the sample was cooled with waterfollowed by aging treatment for 8 hours at 175° C. and cooling in air.

In addition, heat treatment of sample G consisted of solution heattreatment for 2 hours at 530° C. followed by cooling with water, andthen aging treatment for 26 hours at 190° C. followed by cooling in air.

Sample production was completed with this heat treatment.

Furthermore, T1 treatment was performed on the other samples consistingof cooling after the hot extrusion step followed by natural aging.

<Evaluation>

Samples A through L produced by going through each of the stepsdescribed above were evaluated according to the procedures indicatedbelow.

Furthermore, samples F and G were evaluated using the T6 materials onwhich the above heat treatment was performed, while the other samples (Athrough E and H through L) were evaluated using T1 materials on whichheat treatment was not performed.

(1) Observation of Microstructure

The microstructure of all samples A through L were observed for the Lcross-section (parallel to the direction of extrusion) and Tcross-section (perpendicular to the direction of extrusion) at thecenter of the extruded materials.

As a result, all of the samples were confirmed to have a uniform, finestructure.

(2) Tensile Test

The tensile test was performed under two temperature conditions of roomtemperature and 250° C.

The tensile test at room temperature was performed on two test pieces(n=2) for all samples A through L. In addition, the tensile test at 250°C. was performed on two test pieces (n=2) for 8 types of samplesexcluding samples A and C through E.

Furthermore, although all of the tensile tests were performed by usingcylindrical test pieces having a diameter at the parallel portion of 6mm, in the case of tensile tests at 250° C., testing was performed afterholding the test piece at 250° C. for 100 hours.

The test results are shown in Table 3.

TABLE 3 0.2% yield Tensile Rupture Sample Heat strength strengthelongation Temperature No. treatment (MPa) (MPa) (%) Remarks Room A T1 56 105 40 Comparative alloy Temperature B T1  62 112 39 Alloy ofpresent invention C T1  64 114 33 Alloy of present invention D T1  70117 22 Alloy of present invention E T1  80 110  8 Comparative alloy F T6278 307 49 Alloy of present invention G T6 291 426 27 Alloy of presentinvention H T1 165 262 60 Comparative alloy I T1 175 271 21 Alloy ofpresent invention J T1 184 270 18 Alloy of present invention K T1 199281 13 Alloy of present invention L T1 206 267  5 Comparative alloy 250°C. B T1  32  48 36 Alloy of present invention (after holding F T6  74 98 23 Alloy of present invention for 100 hours) G T6 134 185 13 Alloyof present invention H T1  96 143 23 Comparative alloy I T1 107 149 20Alloy of present invention J T1 107 153 12 Alloy of present invention KT1 112 160 12 Alloy of present invention L T1 115 150 10 Comparativealloy

In looking at the experimental results of Table 3, 0.2% yield strengthwas within the range of 56 MPa (sample A) to 291 MPa (sample G) at roomtemperature, and within the range of 32 MPa (sample B) to 134 MPa(sample G) at a high temperature of 250° C.

In addition, tensile strength was within the range of 105 MPa (sample A)to 426 MPa (sample G) at room temperature, and within the range of 48MPa (sample B) to 185 MPa (sample G) at a high temperature of 250° C.Thus, not only at room temperature, but also at a high temperature, thetensile strength of these samples were superior to the boral tensilestrength of 41 MPa (see Table 4).

Continuing, in looking at rupture elongation, values were within therange of 10% (sample L) to 60% (sample H) at room temperature, andwithin the range of 10% (sample L) to 36% (sample B) at a hightemperature of 250° C. Thus, results were demonstrated that weresuperior to boral elongation of 1.2% (see Table 4) at both temperatureconditions.

FIGS. 1 and 2 are graphs showing the effect of temperature on tensilecharacteristics. Both graphs consist of a plot of the values of samplesF, G and I (each containing an added amount of B of 2.3% by weight)based on the test results shown in Table 3. In looking at these graphs,although sample G exhibits the highest values for both 0.2% yieldstrength and tensile strength, since the slope is relatively large, thissample can be seen to be susceptible to the effects of increasingtemperature.

In addition, although sample I exhibited the lowest values at roomtemperature for both 0.2% yield strength and tensile strength, the slopeaccompanying rising temperature is the smallest. Consequently, at a hightemperature of 250° C., it changes places with sample F, indicating thatof the three samples, sample I is least affected by temperature.

Furthermore, the slope of sample F is particularly large for 0.2% yieldstrength, indicating that it is susceptible to the effects of risingtemperature.

Continuing, the graphs of FIGS. 3 through 5 indicate the effect of theamount of B added (wt %) on tensile test results.

FIG. 3 respectively indicates the plots of 0.2% yield strength (MPa),tensile strength (MPa) and rupture elongation (%) (see Table 3) usingroom temperature conditions for pure Al-based samples A through E. Inlooking at this graph, as the amount of B added increases, 0.2% yieldstrength (MPa), indicated with narrow broken lines, and tensile strength(MPa), indicated with a solid line, increase, while conversely, ruptureelongation (%), indicated with broke lines, decreases.

FIG. 4 is a graph respectively indicating the plots of 0.2% yieldstrength (MPa), tensile strength (MPa) and rupture elongation (%) (seeTable 3) using room temperature conditions for Fe-based Al (Al—6Fe)samples H through L. In looking at this graph, as the amount of B addedincreases, 0.2% yield strength (MPa), indicated with narrow brokenlines, and tensile strength (MPa), indicated with a solid line, increasein the same manner as FIG. 3. However, although rupture elongation (%),indicated with broken lines, decreases suddenly due to addition of 2.3%by weight B as compared with not adding B, the amount of that decreaseis small even when the amount of B added is increased from 2.3% byweight to 4.7% by weight.

FIG. 5 is a graph respectively indicating the plots of 0.2% yieldstrength (MPa), tensile strength (MPa) and rupture elongation (%) usinghigh temperature conditions of 250° C. for the same Fe-based Al (Al—6Fe)samples H through L as in FIG. 4. In looking at this graph, as theamount of B added increases, 0.2% yield strength (MPa), indicated withnarrow broken lines, and tensile strength (MPa), indicated with a solidline, increase in the same manner as in FIGS. 3 and 4. In addition, thephenomenon of FIG. 4 in which rupture elongation (%), indicated withbroken lines, decreases suddenly due to addition of B at 2.3% by weightas compared with not adding B is no longer observed, and although thevalues are low overall, a tendency to decrease gradually with increasingamounts of B is indicated in the same manner as FIG. 3.

It can be confirmed from the above three graphs (FIGS. 3 through 5) thatthere is a common trend in which, when the amount of B₄C particlesexceeds 9% in terms of the amount of B, regardless of the composition ofthe matrix, 0.2% yield strength is hardly improved at all while ruptureelongation decreases suddenly, and accompanying this decrease, tensilestrength also decreases. Although all of the materials exhibited higherelongation than, for example, boral (see Table 4), in the case of, forexample, assuming that these materials were actually used as structuralmaterials of a nuclear reactor or spend nuclear fuel container, it canbe concluded that normal temperature elongation of 10% or more isconsidered to be the minimum required value in consideration ofreliability, and that the amount of B₄C added which is able to satisfythis is 9% or less in terms of the amount of B.

Although there were no problems observed in terms of strength orductility for those samples containing low amounts of B, since the lowerlimit of the amount added is determined spontaneously from the requiredneutron absorbing power, that value is 1.5% by weight as the amount of Bas was previously mentioned.

Among the above test results of Table 3, the amount of B (wt %), tensilestrength (MPa) and elongation (%) were extracted and shown in thefollowing Table 4 for six types of samples consisting of samples B, C,F, G, I and J (each having an amount of B added of 2.3 or 4.7% byweight). These were then compared with each of the values of products ofthe prior art obtained by melting methods. Furthermore, the values fortensile strength and elongation shown in Table 4 were obtained at roomtemperature.

TABLE 4 Amount Tensile of B strength Elongation Material (wt %) (MPa)(%) Present Invention Pure Al composite material 2.3 112 39 (Sample B)Pure Al composite material 4.7 114 33 (Sample C) Al—Mg—Si-basedcomposite material 2.3 307 49 (Sample F) Al—Cu-based composite material2.3 429 27 (Sample G) Al—Fe-based composite material 2.3 271 21 (SampleI) Al—Fe-based composite material 4.7 270 18 (Sample J) Prior artAl—Mg-based alloy 0.9 245 20 Al—Mg—Si-based alloy 0.9 270 12Al—Zn—Mg-based alloy 0.9 500 11 Al—Cu-based alloy 0.9 370 15 Al—Mn-basedalloy 0.9 150 11 Boral 27.3   41   1.2

When first comparing the amount of B added, the amount of B added in thearticles of the present invention is 2.3 or 4.7% by weight, and becausethe amount of B added is greater than each of the Al alloys containing0.9% by weight, these composite materials have high neutron absorbingpower. In addition, although the amount of B added in boral is extremelyhigh at 27.3% by weight, since the tensile strength and elongationvalues described below are extremely low, this material can beunderstood to lack adequate workability.

Next, in comparing tensile strength, among the articles of the presentinvention, the pure Al composite material containing 2.3% by weight B(sample B) exhibited the lowest tensile strength of 112 MPa, while amongthe articles of the prior art, Al—Mn-based alloy demonstrated the lowesttensile strength of 150 MPa. However, since sample B contained a higheradded amount of B than the article of the prior art, it has superiorneutron absorbing power. In addition, since it also exhibited elongationthat was significantly higher than that of the prior art by 20%, it isable to withstand practical use in terms of workability. In comparisonwith boral in particular, since both tensile strength and elongationcharacteristics are extremely high, sample B can be understood to besuperior in terms of workability.

Furthermore, in the case of limiting the base to Al alloy, theAl—Fe-based composite material containing 4.7% by weight B (sample J)exhibited the lowest value for tensile strength, and that value was 270MPa.

In addition, the article of the present invention that exhibited themost superior tensile strength was the Al—Cu-based composite materialcontaining 2.3% by weight B (sample G), and that value was 429 MPa. Incontrast, although the Al—Zn—Mg-based alloy exhibited the most superiortensile strength among the articles of the prior art at 500 MPa, theelongation in this case was 11%, which is lower than 18%, which is thelowest value among the articles of the present invention shown in Table4. This trend, namely the trend of having low elongation (11-20%)relative to high tensile strength, is common to aluminum alloyscontaining B of the prior art, and when the B content is taken intoconsideration, the elongation of the articles of the prior art can besaid to be low overall as compared with the elongation values (18-49%)of the articles of the present invention.

Next, on the basis of Table 4, a comparison is made between aluminumcomposite materials (articles of the present invention) and aluminumalloys (articles of the prior art) of the same system.

To begin with, when comparing an Al—Mg—Si-based composite material(sample F) and Al—Mg—Si-based alloy, the article of the presentinvention demonstrated superior values in terms of the amount of B,tensile strength and elongation. Namely, the amount of B was 2.3% byweight as compared with 0.9%, tensile strength was 307 MPa as comparedwith 270 MPa, and elongation was 49% as compared with 12%, thusindicating that the values for all of these parameters are higher forthe article of the present invention.

Continuing, when Al—Cu-based composite material (sample G) was comparedwith Al—Cu-based alloy, in this case as well, the article of the presentinvention exhibited superior values for the amount of B, tensilestrength and elongation. Namely, the amount of B was 2.3% by weight ascompared with 0.9% by weight, tensile strength was 429 MPa as comparedwith 370 MPa, and elongation was 27% as compared with 15%, thusindicating that the values for all of these parameters are higher forthe article of the present invention.

In this manner, since the aluminum composite material of the presentinvention allows the addition of a large amount of B while also havingsuperior tensile characteristics such as tensile strength andelongation, a high degree of workability can be obtained.

In particular, when considering use as the structural material of aspent nuclear fuel transport container or storage container and soforth, although it is desirable to have mechanical properties of tensilestrength of 98 MPa and elongation of 10% or more at 250° C., based onthe results of testing at 250° C., use of aluminum alloy powder otherthan pure Al powder for the base was able to be confirmed to allow thisobjective to be nearly completely achieved.

Example 2

<Powder Classification>

JIS6N01 composition powder produced by air atomization was classified tovarious sizes with a sieve. The sieve sizes used along with the meanparticle size below the sieve and the classification yield in each caseare shown in Table 5.

TABLE 5 Mean particle Classification Sieve size size below sieve yield(μm) (μm) (%) 355 162 99 250 140 88 180 120 60 105  52 21  45  21  5  32 5  3

Although particle size distribution has the potential to fluctuateslightly depending on the alloy composition and atomization conditions,it was able to be confirmed that, as sieve size became smaller,classification yield decreased rapidly. If assuming the premise of usingat the industrial level, it must be unavoidably concluded that the useof powder having a particle size of 45 μm or less, at which theclassification yield falls to a single digit, would be unrealistic.

<Sample Production>

6N01 powder having each of the particle sizes shown in Table 5 and fivetypes of B₄C particles shown in Table 1 were mixed in the combinationsshown in Table 6. The amount of B₄C added was 3% by weight in all cases(2.3% by weight as B), and the mixing time was 10-15 minutes in the samemanner as Example 1.

Powder for which mixing was completed was charged into a can followingthe same procedure as Example 1 followed by vacuum heating degassing andextrusion to obtain an extruded material having a cross-sectional shapemeasuring 48 mm×12 mm. Heat treatment was not performed.

TABLE 6 Mean particle size Mean particle of 6N01 powder used size of B₄Cused No. (μm) (μm)  1 5 9 Alloy of present invention  2 5 23 Alloy ofpresent invention  3 5 59 Alloy of present invention  4 21 9 Alloy ofpresent invention  5 21 23 Alloy of present invention  6 21 59 Alloy ofpresent invention  7 100 9 Alloy of present invention  8 100 23 Alloy ofpresent invention  9 100 59 Alloy of present invention 10 149 9 Alloy ofpresent invention 11 149 23 Alloy of present invention 12 149 59 Alloyof present invention 13 5 0.8 Comparative alloy 14 5 72 Comparativealloy 15 149 0.8 Comparative alloy 16 149 72 Comparative alloy 17 162 9Comparative alloy 18 162 59 Comparative alloy

<Evaluation>

(1) Observation of Microstructure

The images of the microstructures of L cross-sections (parallel to thedirection of extrusion) were analyzed for the respective cross-sectioncenters and exterior portions of the head section, middle section andtail section of each extruded material to investigate localizedaggregation of B₄C particles along with overall distribution uniformity.

More specifically, measurement of the surface area ratio of B₄Cparticles at each observation site was performed for five fields each(with each field measuring 1 mm×1 mm). (Since the specific gravity ofB₄C is roughly 2.51, the weight percentage of B₄C in the aluminum alloycan be estimated with Vol %×2.51/2.7 when taking the specific gravity ofpure Al to be 2.7. On the other hand, the surface area ratio of B₄C in across-section can be assumed to be nearly equal to Vol %. Accordingly,the standard value for the surface area ratio of B₄C is taken to be3%×2.7/2.51=2.8%.)

In the case there was even one point in a single field at which the B₄Csurface area ratio reached twice the standard value (namely, 5.6%), theextruded material was judged to have aggregation, and in the case themean value of the surface area ratios of 5 fields at each site deviatedfrom the standard value by ±0.5% (namely within the range of 2.3-3.3%),the extruded material was judged to have non-uniform distribution. Thoseresults are shown in Table 7.

TABLE 7 Mean particle Mean particle size of size of 6N01 powder used B₄Cused Evaluation of B₄C distribution No. (μm) (μm) AggregationNon-uniformity  1  5  9 No Uniform Alloy of present invention  2  5 23No Uniform Alloy of present invention  3  5 59 No Uniform Alloy ofpresent invention  4  21  9 No Uniform Alloy of present invention  5  2123 No Uniform Alloy of present invention  6  21 59 No Uniform Alloy ofpresent invention  7 100  9 No Uniform Alloy of present invention  8 10023 No Uniform Alloy of present invention  9 100 59 No Uniform Alloy ofpresent invention 10 149  9 No Uniform Alloy of present invention 11 14923 No Uniform Alloy of present invention 12 149 59 No Uniform Alloy ofpresent invention 13  5   0.8 Yes Uniform Comparative alloy 14  5 72 NoNon-uniform Comparative alloy 15 149   0.8 Yes Uniform Comparative alloy16 149 72 No Uniform Comparative alloy 17 162  9 No Uniform Comparativealloy 18 162 59 No Uniform Comparative alloy

In contrast satisfactory B₄C distribution being obtained for all of thealloys of the present invention, in comparative alloys nos. 13 and 15,which used fine B₄C particles having mean particle size of 0.8 μm, localaggregation occurred. In addition, in the case of no. 14, in whichcoarse B₄C particles having a mean particle size of 72 μm were added tofine Al alloy powder having a mean particle size of 5 μm, non-uniformparticle distribution occurred between each site within the extrudedmaterial.

(2) Room Temperature Tensile Test

Each of the produced extruded materials were submitted to tensiletesting at room temperature. The shape of the test pieces was the sameas in Example 1, namely cylindrical test pieces having a diameter of 6mm at the parallel portion. The results are shown in Table 8.

As was described in Example 1, when the standard value for acceptance orrejection was taken to be rupture elongation of 10% or more, all of thealloys of the present invention were determined to satisfy thisstandard. In contrast, in the case of comparative materials nos. 14 and16, in which coarse B₄C particles having a mean particle size of 72 μmwere added, and nos. 17 and 18, in which the mean particle size of thebase powder was large at 162 μm, there were remarkable decreases inductility, and these materials were unable to satisfy the abovestandard.

In summary of the above results, in order to obtain a material havingboth a uniform structure free of aggregation of B₄C (namely, uniformneutron absorbing power) and the required ductility for ensuringreliability as a structure material, it was able to be confirmed that itis imperative to control the particle size of the base powder as well asthe particle size of the added particles to within the range of thepresent invention.

TABLE 8 Mean particle Mean particle Test Results size of size of 0.2%yield Tensile Rupture 6N01 powder used B₄C used strength strengthelongation No. (μm) (μm) (MPa) (MPa) (%)  1  5  9 83 151 16 Alloy ofpresent invention  2  5 23 80 143 13 Alloy of present invention  3  5 5973 129 11 Alloy of present invention  4  21  9 81 153 22 Alloy ofpresent invention  5  21 23 79 150 19 Alloy of present invention  6  2159 71 132 14 Alloy of present invention  7 100  9 75 148 21 Alloy ofpresent invention  8 100 23 76 149 15 Alloy of present invention  9 10059 76 141 14 Alloy of present invention 10 149  9 70 143 14 Alloy ofpresent invention 11 149 23 68 134 12 Alloy of present invention 12 14959 62 131 11 Alloy of present invention 13  5   0.8 87 157 21Comparative alloy 14  5 72 72 123  7 Comparative alloy 15 149   0.8 75147 11 Comparative alloy 16 149 72 56 129  8 Comparative alloy 17 162  970 142  9 Comparative alloy 18 162 59 63 125  7 Comparative alloy

Example 3

<Sample Production>

Billets were produced with the compositions and processes shown in Table9 and submitted to extrusion at 430° C.

The pure Al and Al—6Fe alloy powder used here were the same as thoseused in Example 1. The former consisted of air atomized powderclassified to 250 μm or less (mean particle size: 118 μm), while thelatter consisted of N₂ gas atomized powder classified to 150 μm or less(mean particle size: 95 μm). In addition, the B₄C particles used had amean particle size of 23 μm.

The powder blended into each composition was mixed for 20 minutes with across rotary mixer. In the following processes A through E, canning andvacuum heating degassing were performed using the same procedures asExamples 1 and 2 to produce billets that were then submitted toextrusion. At this time, the vacuum degassing temperature was 350° C. inA, 480° C. in B, 550° C. in C, 300° C. in D and 600° C. in E, andextrusion was performed at 430° C. throughout. The extruded shape wasthe same as in Example 1, measuring 48 mm×12 mm.

In process F, after heating the mixed powder for 2 hours in a furnace at200° C. in which the pressure was reduced to 4-5 Torr, the powder wasfilled into a rubber mold in air followed by CIP (cold hydrostaticcompression) molding. The resulting molded article had a density ofabout 75% (porosity: 25%). It was then heated at 430° in air andsubmitted to extrusion. The extruded shape measured 48 mm×12 mm.

In process G, the mixed powder was CIP molded directly followed byheating to 430° C. in air and extruding. The extruded shape measured 48mm×12 mm.

TABLE 9 Amount of B₄C added Powder Used (wt %) Process Remarks Pure Al 3A (350° C. degassing) Alloy of present invention (<250 μm) 3 B (480° C.degassing) Alloy of present invention 3 C (550° C. degassing) Alloy ofpresent invention Al—6Fe 3 A (350° C. degassing) Alloy of presentinvention (<150 μm) 3 B (480° C. degassing) Alloy of present invention 3C (550° C. degassing) Alloy of present invention Pure Al 3 D (300° C.degassing) Comparative alloy (<250 μm) 3 F (degassing without canning)Comparative alloy 3 G (no degassing) Comparative alloy Al—6Fe 3 D (300°C. degassing) Comparative alloy (<150 μm) 3 E (600° C. degassing)Comparative alloy

<Evaluation>

Observation of the surface of the extruded materials, room temperaturetensile tests in the lengthwise direction, and measurement of the amountof hydrogen gas were performed on each of the extruded materials.Measurement of the amount of gas was performed vacuum meltextrusion-mass analysis in compliance with LIS A06.

The results are shown in Table 10. In contrast to satisfactory resultsbeing obtained for extruded material surface properties, mechanicalproperties and amount of hydrogen gas in materials produced usingprocesses A through C, which are within the scope of claim for patent ofthe present invention, the following problems occurred in the case ofthe comparative alloys.

In process D, in which degassing was performed at a temperature lowerthan the scope of the present invention, hydrogen on the powder surfacethat was unable to be removed was released during extrusion, causing theso-called “blistering” defect in which air bubbles form immediatelybeneath the facing of the extruded material.

Although the high strength of the Al—Fe-based alloy was realized bydispersing intermetallic compound particles finely and uniformly due torapid cooling solidification effects, in process E in which degassingwas performed at an extremely high temperature, the mean particle sizesof these compounds increased, causing a sudden decrease in strength andductility.

In process F, in which degassing was performed without canning, inaddition to being unable to avoid a step in which the powder is exposedto the air until the time of extrusion, due to the extremely lowdegassing temperature, the amount of hydrogen gas was near that of thecase of not performing degassing, and together with blistering occurringon the surface of the extruded materials, both strength and ductilityexhibited low values.

In process G, in which degassing was not performed, an extremely largeamount of hydrogen gas remained, which in addition to causingblistering, resulted in low values for strength and ductility.

On the basis of these results, it was confirmed that, in order toproduce Al alloy composite materials having satisfactory characteristicsregardless of which matrix alloy is used, it is imperative to use theproduction method described in the present invention.

TABLE 10 Tensile Test Amount of Extruded Yield Tensile hydrogen materialstrength strength Elongation gas Matrix Process surface (MPa) (MPa) (%)(cc/100 g) Remarks Pure Al A (350° C. degas) Good  58 105 21 9.0 Alloyof present invention B (480° C. degas) Good  62 112 39 3.1 Alloy ofpresent invention C (550° C. degas) Good  63 114 41 2.9 Alloy of presentinvention Al—6Fe A (350° C. degas) Good 201 279 10 8.8 Alloy of presentinvention B (480° C. degas) Good 199 281 13 3.0 Alloy of presentinvention C (550° C. degas) Good 195 282 15 2.9 Alloy of present Pure AlD (300° C. degas) Blister  49  88 11 17.1  Comparative alloy F (degas,no can) Blister  43  79 17 31.0  Comparative alloy G (no degas) Blister 41  78  7 39.2  Comparative alloy Al—6Fe D (300° C. degas) Blister 224291  8 16.8  Comparative alloy E (600° C. degas) Good  91 127  7 2.9Comparative alloy

Example 4

3% by weight (2.3% by weight as B) of B₄C particles having a meanparticle size of 23 μm were added to a pure Al powder produced by airatomization and classified to 250 μm or less, followed by the productionof an extruded material having a cross-sectional shape measuring 48mm×12 mm using the same method as in Examples 1 and 2. The tensilecharacteristics of the resulting extruded material consisted of yieldstrength of 62 MPa, tensile strength of 112 MPa and rupture elongationof 39%.

3% by weight of B₄C was wrapped in aluminum foil and placed into a pureAl melt having a purity of 99.7% melted in a high-frequency meltingfurnace followed immediately by stirring well in an attempt to produce acomposite material. However, due to the extremely poor wettability ofthe B₄C particles, the majority of the particles ended up floating tothe melt surface. Accordingly, production of Al—B₄C composite materialsby melt stirring was judged to be difficult.

Pure Al metal having a purity of 99.7% and pure B were blended so thatthe amount of B was 2.3% by weight, melted in a high-frequency meltingfurnace and cast into billets having a diameter of 90 mm followed bysubmitting to extrusion. The extruded shape measured 48 mm×12 mm. Sincethe melting temperature of B is extremely high at 2092° C., it wasconsidered to be difficult to handle with ordinary Al alloy equipment(even if an intermediate alloy of Al—B is used, although the degree ofthe problem is different, the problem remains the same). In addition,the resulting extruded material had low elongation of 3.1%, and wasjudged to be difficult to use as a structural material.

On the basis of the above results, it was able to be confirmed that, inorder to obtain a material containing a high concentration of B whilealso having high strength and ductility, production of a compositematerial by a powder method is the most feasible as described in thepresent invention.

INDUSTRIAL APPLICABILITY

The production method of an Al composite material having neutronabsorbing power of the present invention as described above offers theadvantages described below.

An aluminum composite material produced using a powder metallurgytechnique in the form of pressurized sintering after adding B powder orpowder of a B compound having neutron absorbing power to an aluminum oraluminum alloy powder and then mixing allows the addition of a largeamount (1.5-9% by weight) of B or B compound as compared with meltingmethods of the prior art.

Consequently, the ability to absorb high-speed neutrons in particular isimproved by increasing the amount of B added, and in addition to havinghigh tensile strength at room temperature on the order of 112-426 MPa,an aluminum composite material can be provided that has extremelysuperior elongation of 13-50%. In addition, this aluminum compositematerial also has characteristics consisting of tensile strength of48-185 MPa and elongation of 12-36% even at a high temperature of 250°C. Namely, the use of the present invention makes it possible to obtainan aluminum composite material that is suitable for use as a structuralmaterial, which in addition to having high neutron absorbing power,offers superior balance between strength and ductility.

Furthermore, in addition to the each of the characteristics describedabove, the ability to absorb low-speed neutrons can also be imparted bysuitably adding Gd or Gd compound having superior low-speed neutronabsorbing power.

What is claimed is:
 1. An aluminum composite material having neutronabsorbing power, wherein the aluminum composite material contains an Alor an Al alloy matrix phase, wherein the Al or Al alloy is selected fromthe group consisting of pure aluminum metal, Al—Mg—Si-based alloys,Al—Zn—Mg-based alloys, Al—Fe-based alloys, and Al—Mn-based alloys; and Bor a B compound having neutron absorbing power in an amount such thatthe proportion of B is 1.5% by weight or more to 9% by weight or less,and the aluminum composite material has been pressurized sintered,wherein said pressurized sintering is at least one of hot extrusion, hotrolling, hot hydrostatic pressing and hot pressing.
 2. A productionmethod of an aluminum composite material having neutron absorbing powercomprising: adding a B or B compound powder having neutron absorbingpower in an amount such that the proportion of B is 1.5% by weight ormore to 9% by weight or less to an Al or Al alloy powder, wherein the Alor Al alloy is selected from the group consisting of pure aluminummetal, Al—Mg—Si-based alloys, Al—Zn—Mg-based alloys, Al—Fe-based alloys,and Al—Mn-based alloys; and pressurized sintering the powder, whereinsaid pressurized sintering is at least one of hot extrusion, hotrolling, hot hydrostatic pressing and hot pressing.
 3. The productionmethod of an aluminum composite material having neutron absorbing poweraccording to claim 2, wherein said Al or Al alloy powder is a rapidlysolidified powder.
 4. The production method of an aluminum compositematerial having neutron absorbing power according to claim 2, whereinboron carbide (B₄C) particles are used as said B compound particles. 5.The production method of an aluminum composite material having neutronabsorbing power according to claim 2, wherein the mean particle size ofsaid Al or Al alloy powder is 5 to 150 μm, and the B compound particlesused are B₄C particles having a mean particle size of 1 to 60 μm.
 6. Theproduction method of an aluminum composite material having neutronabsorbing power according to claim 2, wherein the powder is charged intoa can after heating the inside of the can to contain the powder to350-550° C. followed by vacuum degassing, and while maintaining thevacuum inside the can, the powder is subjected to pressurized sintering.7. The production method of an aluminum composite material havingneutron absorbing power according to claim 2, wherein heat treatment isperformed following said pressurized sintering.
 8. The production methodof an aluminum composite material having neutron absorbing poweraccording to claim 3, wherein boron carbide (B₄C) particles are used assaid B compound particles.
 9. The production method of an aluminumcomposite material having neutron absorbing power according to claim 3,wherein the mean particle size of said Al or Al alloy powder is 5 to 150μm, and the B compound particles used are B₄C particles having a meanparticle size of 1 to 60 μm.
 10. The production method of an aluminumcomposite material having neutron absorbing power according to claim 4,wherein the mean particle size of said Al or Al alloy powder is 5 to 150μm, and the B compound particles used are B₄C particles having a meanparticle size of 1 to 60 μm.
 11. The production method of an aluminumcomposite material having neutron absorbing power according to claim 8,wherein the mean particle size of said Al or Al alloy powder is 5 to 150μm, and the B compound particles used are B₄C particles having a meanparticle size of 1 to 60 μm.
 12. The production method of an aluminumcomposite material having neutron absorbing power according to claim 3,wherein the powder is charged into a can after heating the inside of thecan to contain the powder to 350-550° C. followed by vacuum degassing,and while maintaining the vacuum inside the can, the powder is subjectedto pressurized sintering.
 13. The production method of an aluminumcomposite material having neutron absorbing power according to claim 4,wherein the powder is charged into a can after heating the inside of thecan to contain the powder to 350-550° C. followed by vacuum degassing,and while maintaining the vacuum inside the can, the powder is subjectedto pressurized sintering.
 14. The production method of an aluminumcomposite material having neutron absorbing power according to claim 5,wherein the powder is charged into a can after heating the inside of thecan to contain the powder to 350-550° C. followed by vacuum degassing,and while maintaining the vacuum inside the can, the powder is subjectedto pressurized sintering.
 15. The production method of an aluminumcomposite material having neutron absorbing power according to claim 8,wherein the powder is charged into a can after heating the inside of thecan to contain the powder to 350-550° C. followed by vacuum degassing,and while maintaining the vacuum inside the can, the powder is subjectedto pressurized sintering.
 16. The production method of an aluminumcomposite material having neutron absorbing power according to claim 3,wherein heat treatment is performed following said pressurizedsintering.
 17. The production method of an aluminum composite materialhaving neutron absorbing power according to claim 4, wherein heattreatment is performed following said pressurized sintering.
 18. Theproduction method of an aluminum composite material having neutronabsorbing power according to claim 5, wherein heat treatment isperformed following said pressurized sintering.
 19. The productionmethod of an aluminum composite material having neutron absorbing poweraccording to claim 8, wherein heat treatment is performed following saidpressurized sintering.
 20. An aluminum composite material having neutronabsorbing power, wherein the aluminum composite material contains an Alor an Al alloy matrix phase, B₄C having neutron absorbing power in anamount such that the proportion of B is 1.5% by weight or more to 9% byweight or less, and the aluminum composite material has been obtained byadding B₄C particles having a mean particle size of 1 to 60 μm to Al orAl alloy powder having a mean particle size of said is 5 to 150 μm, andthen pressure sintering, wherein said pressurized sintering is at leastone of hot extrusion, hot rolling, hot hydrostatic pressing and hotpressing.
 21. An aluminum composite material having neutron absorbingpower, wherein the aluminum composite material contains an Al or an Alalloy matrix phase, B or a B compound having neutron absorbing power inan amount such that the proportion of B is 1.5% by weight or more to 9%by weight or less, and the aluminum composite material has been obtainedby adding the B or B compound powder to the Al or Al alloy powder,charging the powder into a can after heating the inside of the can tocontain the powder to 350-550° C. followed by vacuum degassing, andwhile maintaining the vacuum inside the can, subjecting the powder topressurized sintering, wherein said pressurized sintering is at leastone of hot extrusion, hot rolling, hot hydrostatic pressing and hotpressing.
 22. The aluminum composite material according to claim 20,wherein heat treatment is performed following said pressurizedsintering.
 23. The aluminum composite material according to claim 21,wherein heat treatment is performed following said pressurizedsintering.
 24. The aluminum composite material according to claim 1,wherein pure aluminum metal is used as the matrix.
 25. The aluminumcomposite material according to claim 1, wherein an Al alloy selectedfrom the group consisting of Al—Mg—Si, Al—Zn—Mg, Al—Fe, and Al—Mn basedalloys is used as the matrix.
 26. The production method of an aluminumcomposite material having neutron absorbing power according to claim 2,wherein an Al alloy selected from the group consisting of Al—Mg—Si,Al—Zn—Mg, Al—Fe, and Al—Mn based alloys is used as the matrix.
 27. Thealuminum composite material according to claim 1, which has a thicknessof from about 5 to 30 mm.
 28. An aluminum composite material havingneutron absorbing power, wherein the aluminum composite materialcontains an Al alloy matrix phase, wherein the Al alloy is selected fromthe group consisting of Al—Mg—Si-based alloys; and B or a B compoundhaving neutron absorbing power in an amount such that the proportion ofB is 1.5% by weight or more to 5% by weight or less, and the aluminumcomposite material has been pressurized sintered, wherein saidpressurized sintering is at least one of hot extrusion, hot rolling, hothydrostatic pressing and hot pressing.
 29. A production method of analuminum composite material having neutron absorbing power comprising:adding a B or B compound powder having neutron absorbing power in anamount such that the proportion of B is 1.5% by weight or more to 5% byweight or less to an Al alloy powder, wherein the Al alloy is selectedfrom the group consisting of Al—Mg—Si-based alloys; and pressurizedsintering the powder, wherein said pressurized sintering is at least oneof hot extrusion, hot rolling, hot hydrostatic pressing and hotpressing.